<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <input type="text" id="username"> <input type="checkbox" name="" id="remember"> 记住用户名

</body>

<script>
    let username = document.querySelector('#username');
    let remember = document.querySelector('#remember');
    if (localStorage.getItem('username')) {
        username.value = localStorage.getItem('username');
        remember.checked = true;
    }
    remember.addEventListener('change', function() {
        if (this.checked) {
            localStorage.setItem('username', username.value);
        } else {
            localStorage.removeItem('username');
        }
    })
</script>

<!-- <script>
    var username = document.querySelector('#username');
    var remember = document.querySelector('#remember');
    if (localStorage.getItem('username')) {
        username.value = localStorage.getItem('username');
        remember.checked = true;
    }
    remember.addEventListener('change', function() {
        if (this.checked) {
            localStorage.setItem('username', username.value)
        } else {
            localStorage.removeItem('username');
        }
    })
</script> -->